This invention relates to a weatherseal for an opening in a structure the interior of which is to be protected against wind and rain. The weatherseal preferably having a relatively soft extrudate body, a portion of which is coated with a slip-coating of relatively harder elastomer, is formed as an extrudate of relatively hard elastomer thermally bonded as a slip-coating and forming an integral portion of a softer polymer. The slip-coating not only exhibits low frictional characteristics and high abrasion resistance but also remarkable softness compared to that of conventional slip-coatings.
The Problem
Though available elastomers of extrudable thermoplastic vulcanizates (TPVs) are commonly used to produce weatherseals, the ever-increasing demands of the marketplace seeks weatherseals with improved properties. Properties which are currently accepted but seek improvement are found in TPV weatherseals having an elongate body or base portion which have been co-extruded with slip-coatings having a hardness of at least 50 Shore D, Taber abrasion resistance measured at 500 cycles of at least 50, and a coefficient of friction greater than about 0.3. Though it is known that any one of the foregoing properties can be lowered, it is not known how to lower all three properties and still produce a marketable weatherseal.
The goal is to produce a slip-coating which provides an exceptionally good seal against entry of wind, snow and rain because of a critical combination of three specific properties, namely softness, good abrasion resistance, and low coefficients of friction; and to formulate the slip-coating containing a TPV which allows it to be thermally bonded to the body so as to become an integral part of it, and to be pigmented or painted with colors of choice.
The term xe2x80x9celastomerxe2x80x9d is used in the broad sense, in that the cured blend is extrudable as a dense solid TPV essentially free of macroscopic voids, or a dense foam having a density in the range greater than about 80% of that of the dense solid, and the TPV is re-processable, unlike a thermoset resin. By xe2x80x9cextrudablexe2x80x9d is meant that a vulcanized blend can be processed in an available, commercial extruder or injection molding machine which provides internal mixing at a temperature in the range from about 180xc2x0 C. to 240xc2x0 C. with a residence time less than 5 min, preferably in the range from 30 sec to 2 min. In such TPVs, which are xe2x80x9cself-curedxe2x80x9d and not physical blends, their combination of desirable elastic and thermoplastic properties depends on the respective amounts of xe2x80x9chardxe2x80x9d and xe2x80x9csoftxe2x80x9d phases provided by each component, and the properties of each component. The polyolefin phase is the continuous xe2x80x9chardxe2x80x9d phase in which the rubber xe2x80x9csoftxe2x80x9d phase is present as discrete particles. By varying the ratios of the components, one may provide desired hardness/softness, oil and temperature resistance, oxidation resistance, and extrudability, inter alia.
Commonly used weatherseals are provided with a flock or fibrous nap against which the glass of an automobile""s window abuts; though effective, the nap suffers from repeated use, either being abraded away or being worn off. Moreover the process for depositing the nap is complicated and expensive.
The term xe2x80x9cweathersealxe2x80x9d refers to an extrudate of elastomer intended for use in any application where metal or glass parts are used with the extrudate in abutting contact therebetween, typically in the window of a vehicle, or for a belt-line seal for a door. Weatherseals are known to be co-extruded, being formed with a base portion made of a hard polymer, and a support portion made of a soft polymer, either or both of which are coated with a coating which is a blend of two resins having different melting points (see U.S. Pat. No. 5,343,655 to Miyakawa et al). The term xe2x80x9cco-extrudedxe2x80x9d is used herein to describe the substantially concurrent extrusion of a body or support portion from one barrel and the extrusion of an elastomer slip-coating from a second barrel, the slip-coating to be integrally bonded to the body or support portion. The coating may also be provided as a batten surface layer comprising nylon, polyurethane, fluoro-resin, polystyrene or polyolefin containing particles of mica, molybdenum and/or graphite to form a rough surface with projections and recesses (see U.S. Pat. No. 5,441,685). For example a filler of molybdenum disulfide particles provides a tape of a fluorocarbon polymer with lubricity. Adhesively securing a tape of one of the foregoing polymers (as the batten surface) to a base weatherseal requires coating the base with an adhesive, and additional steps; and securing the tape to curved or complex surfaces is difficult. Another coating provided as a batten surface layer has been co-extruded with a guide edging member using small and large particles of nylon 11 and/or 12, or a polyolefin mixed with small and large particles of nylons 6 and/or 66 or a fluorocarbon resin, having high melting points (see U.S. Pat. No. 5,447,671).
Still another weatherseal is provided by coextruding a base polyolefin elastomer to form a support body which is coated with a co-extruded protective film of a mixture consisting of a polyolefin-based resin having low viscosity and high fluidity, and grains of particles of an additive material which is a polyolefin-based resin having high viscosity and low fluidity (see U.S. Pat. No. 5,424,019). More specifically, the base material for the protective film is polyethylene (PE) having a melt flow rate greater than 0.6 g/10 min (ASTM D 1238 190xc2x0 C.) and the additive material is in the form of grains and particles of a high viscosity PE having a melt flow rate less than 0.1 g/10 min.
The co-extrusion and thermal bonding of a slip-coating to a body or base portion of a weatherseal is conventional and essentially the same or similar equipment as used in the ""019 patent is used in the process of this invention. A protective layer may also be provided with a layer of crystalline polyolefin and a rubber, and a layer of an ultrahigh molecular weight polyolefin which contacts the glass (see EP 0 860 314 A1).
Still another slip-coating is provided with a TPV of chosen hardness, typically 50 Shore D, blending it with a thermoplastic polyolefin resin and doctoring the blend with various plasticizers, and fillers such as fatty acid amides and organopolysiloxanes to get the desired low coefficient of friction, also referred to as lubricity, (see Japanese Patent Application No. 7-346094 and JP 9176408A). The effect of the addition of a semicrystalline polyolefin in combination with a plasticizer and a filler to a TPV is improved abrasion resistance and lubricity (low coefficients of friction). There is no suggestion that inclusion of a thermoplastic polyurethane (TPU), normally incompatible with such a TPV, may provide any benefit, particularly when the TPV includes a minor proportion by weight of a semicrystalline polyolefin copolymer. However, not only does the melt-blend of a TPV with a compatibilized TPU exhibit excellent abrasion resistance and lubricity, but it also has the ability to be integrally bonded to a TPV. Moreover, the novel TPV containing the compatibilized TPU can be colored either by inclusion of a pigment of choice, or by being painted with appropriate commercially available paints, particularly urethane-based paints. When the olefin copolymer is omitted from the melt-blend the slip-coating has unacceptable Taber abrasion.
None of the prior art weatherseals provides an elongate body with a coextruded glass-abutting layer which is softer than 50 Shore D but has a Taber abrasion which indicates abrasion damage low enough to indicate that the slip-coating is neither worn away, or torn off. In addition, prior art weatherseals formed with a co-extruded slip-coating deliberately formulated to have a hardness lower than 50 Shore D are found to have unacceptably poor Taber abrasion (measured by ASTM D 1044-94), or poor friction characteristics which cause xe2x80x9cstickingxe2x80x9d of the glass to the weatherseal, particularly on hot days when the glass is exposed to bright sun. If formulated to have a hardness higher than 50 Shore D, the weatherseal tends to leak in locations where the glass does not press against the sealing surface either sufficiently evenly, or firmly. Moreover weatherseals harder than 50 Shore D lack xe2x80x9cgood handxe2x80x9d and fail to be squeak-free on either a hot day or a cold day. No prior art glass-abutting surface has the critical combination of softness, good abrasion resistance and lower coefficients of friction, provided by the weatherseal of this invention.
It is known that PP may be modified by grafting an unsaturated monomer bearing an acid anhydride group to the PP, and reacting the graft (referred to as xe2x80x9cmPPxe2x80x9d) so formed with an a polymer having at least two groups which are reactive to the anhydride group (see U.S. Pat. No. 4,735,992) but there is no suggestion that the reaction product of a mPP and a thermoplastic polyurethane may be incorporated in a melt-blend of a TPV to provide a slip-coating which is uniquely adapted for use on a weatherseal.
It has been discovered that the base of a weatherseal formed from a xe2x80x9cfirst TPVxe2x80x9d, may have thermally bonded to it a slip-coating of a copolymer layer containing thermoplastic polyurethane (TPU); the slip-coating is formed by melt-blending a xe2x80x9csecond TPVxe2x80x9d with a reaction product of (i) a graft copolymer of polypropylene (PP), (ii) a thermoplastic polyurethane (TPU) and (iii) a random copolymer of two or more xcex1-olefins having from 2 to about 12 carbon atoms; the graft copolymer functions as a compatibilizer allowing TPU which is normally incompatible with an olefin-based TPV to be molecularly connected in the slip-coating. The combination of specific properties of the slip-coating is as follows: hardness lower than 50 Shore D, preferably in the range from 85 Shore A to 45 Shore D; a Taber abrasion resistance (measured at 500 cycles) in the range from about 15 to about 50; and coefficients of friction, both static and dynamic, in the range from about 0.1 to 0.4. This combination of properties provides smooth contact with, and release of a glass-abutting or door-abutting surface of the weatherseal; longevity in use; a paintable surface; excellent xe2x80x9cfreeze releasexe2x80x9d, that is minimal sticking of the slip-coating to the surface of the window-glass or door; and no squeak when the window-glass is raised or lowered.
The foregoing combination of properties is found to be provided by a slip-coating comprising (i) an olefin-based thermoplastic elastomer (TPV) having a hardness in the range above 85 Shore A but below 50 Shore D, (ii) a melt-blended reaction product of a graft copolymer of PP and a TPU which is otherwise incompatible with a TPV whether the rubber in the TPV is EPDM or butyl rubber, and (iii) from 5 to 30 parts of an xcex1-olefin copolymer per 100 parts of slip-coating. The reaction product (referred to as mPP-g-TPU) is preferably formed by melt-blending and thermally copolymerizing (i) a minor portion by weight of commercially available pellets, or a powder, of a high molecular weight polypropylene (PP) modified by grafting a monomer bearing an anhydride group (mPP) with (ii) a major portion by weight of commercially available pellets of a compound having at least two groups which are reactive with the anhydride group, preferably thermoplastic polyurethane (TPU). The mPP-g-TPU functions as a compatibilized TPU melt-blended with a second TPV in the slip-coating, allowing it to be thermally bonded to a first TPV extrudate of arbitrary length, and at the same time the mPP-g-TPU functions as a viscosity reducer which reduces the viscosity of the melt-blend (of second TPV with mPP-g-TPU). The ratio of second TPV to mPP-g-TPU is in the range from 20:1 to 1:20. The melt-blend of second TPV and mPP-g-TPU has a viscosity lower than that of the first TPV which is extruded in a cross-section suitable for its intended purpose in the window of a vehicle, or a belt-line seal for a door.